Processes for the preparation of 5-cyanovaleric acid from pentenenitriles by carbonylation in the presence of cobalt carbonyl catalysts are known. See, for example, U.S. Pat. No. 4,508,660 to Sieja where the reaction is carried out in a sulfone solvent, and U.S. Pat. No. 4,060,543 to Weitz, et al., where the reaction is carried out in the presence of basic heterocyclic compounds having a 5-membered or 6-membered nitrogen-containing ring, for example pyridine.
It seems to be recognized in the art that the presence of pyridine in a carbonylation reaction mixture provides an increased yield in the straight chain isomers --See Organic Chemistry and Technology, New Method of Production of Adipic Acid, N. S. Imyanitov and E. N. Rakhlina, Khimicheskaya Promyshlennost, Vol. 19, No. 12, pp. 4-7, 1987 and Chem. Ztg. 111 no 11:317-23 (1987) Hydrocarboxylation of Unsaturated Carboxylic Acids and Esters with Cobalt Carbonyl/Pyridine Complex Catalyst Systems by Bernhard Fell, Institute for Technical Chemistry and Petrochemistry of the RWTH Aachen, and Zilin Jin, Dalian Institute of Technology, Dalian/Peoples Republic of China, and New Syntheses with Carbon Monoxide, edited by J. Falbe; page 252, Springer-Verlag, Berlin Heidelberg, N.Y., 1980.